JP2022547254A - Process for preparation of water-based gel ink with fixed color containing silver nanoparticles - Google Patents

Abstract

The present invention comprises the steps of (i) preparing a gel-based matrix of an aqueous ink, and (ii) adding a silver salt to: - water, - a mixture of at least an alkali metal or alkaline earth metal salt of citrate, - an oxidizing agent, (iii) preparing an aqueous suspension of silver nanoparticles having a fixed color, preferably by mixing with hydrogen peroxide H2O2, - and polyvinylpyrrolidone; adding the aqueous suspension to the aqueous ink gel-based matrix obtained in step (i) with stirring to obtain an aqueous gel ink having a fixed color with silver nanoparticles dispersed therein; A process for preparing an aqueous gel ink having a fixed color, comprising: [Selection figure] None

Description

The present invention provides a process for preparing an aqueous gel ink with a fixed color and containing silver nanoparticles stabilized by polyvinylpyrrolidone obtainable according to the process of the present invention and having a fixed color without any dyes and pigments. It relates to water-based gel ink. The present invention also relates to writing instruments comprising water-based gel inks with fixed colors according to the present invention.

One of the main objectives of the present invention is to replace all types of dyes and pigments normally present in aqueous gel inks, which have the drawback of being expensive and causing high production costs.

Another object of the present invention is to replace all types of dyes and pigments normally present in water-based gel inks, which have the drawback of irritating biological membranes, e.g. skin and eyes, and potentially causing allergies. is.

The inventors have surprisingly found that new water-based inks containing a nanoparticle base are also resistant to UV light, thereby improving photostability over time.

Additionally, silver nanoparticles have antibacterial properties, so the amount of other antibacterial agents can be reduced.

To this end, we replace conventional water-based gel inks containing dyes and pigments with new ones based on nanoparticles, making it possible to obtain new water-based inks with a fixed color when written. We have developed a specific process that is The process developed within the framework of the present invention also presents the advantage of being carried out in an aqueous medium and is therefore an "environmentally friendly process". Furthermore, the process of the invention is carried out in the low temperature range, functions in an ecologically viable manner and also takes into account ecological requirements.

The present invention relates to a process for preparing aqueous gel inks with fixed color,
(i) preparing a gel-based matrix of water-based ink;
(ii) a silver salt:
-water,
- a mixture of at least an alkali metal or alkaline earth metal salt of a citrate, preferably an alkali citrate, and an alkali metal hydride, preferably _NaBH4 ,
- an oxidizing agent, preferably hydrogen peroxide H ₂ O ₂ ,
- and polyvinylpyrrolidone, to prepare an aqueous suspension of silver nanoparticles having a fixed color,
(iii) adding the aqueous suspension of silver nanoparticles obtained in step (ii) to the gel-based matrix of the aqueous ink obtained in step (i) with stirring to disperse the silver nanoparticles therein; obtaining a water-based gel ink having a fixed color in a set state.

The present invention also relates to a process for preparing an aqueous ink, preparing the matrix of the aqueous ink in step (i). The invention also relates to water-based inks obtainable through such processes. Various embodiments described below with respect to the process of preparing an aqueous gel ink and the aqueous gel ink that can be obtained through this process describe the process of preparing an aqueous ink and the aqueous ink thus obtained, in particular the properties and / Or the content can be similarly considered. These embodiments of water-based inks, processes for their preparation, and matrices of water-based inks are also part of the present invention.

According to a preferred embodiment of the present invention, a process for preparing an aqueous gel ink with fixed color comprises:
(i) preparing a gel-based matrix of water-based ink;
(ii) a silver salt:
-water,
- a mixture of at least sodium citrate and sodium borohydride _NaBH4 ,
- hydrogen peroxide H ₂ O ₂ ,
- and polyvinylpyrrolidone, to prepare an aqueous suspension of silver nanoparticles having a fixed color,
(iii) adding the aqueous suspension of silver nanoparticles obtained in step (ii) to the gel-based matrix of the aqueous ink obtained in step (i) with stirring to disperse the silver nanoparticles therein; obtaining a water-based gel ink having a fixed color in a set state.

The process according to the invention makes it possible to obtain aqueous ink compositions exhibiting a plasmonic effect (also called plasmonic effect). Different plasmonic colored compositions can thus be obtained depending on the content of the components used.

For the purposes of the present invention, the term "ink" is intended to mean "writing ink" intended for use in writing instruments, particularly pens. Writing inks should not be confused with "printing inks" that are used in printing presses and do not have the same technical constraints and therefore the same specifications. In fact, the writing ink should not contain solid particles larger in size than the writing instrument's channels, in order to avoid clogging the writing instrument, which would inevitably irreversibly stop writing. . In addition, it should allow an ink flow rate suitable for the writing instrument used, in particular a writing flow rate of 100-500 mg/200 m, in particular a writing flow rate of 150-400 mg/200 m. It should also dry quickly enough to avoid smearing the writing medium. It is also necessary to avoid dye migration (bleeding) problems over time. Accordingly, the inks according to the invention will be suitable for the writing instruments for which they are intended, especially pens.

Furthermore, the "writing ink" should not be too fluid to avoid leakage during writing. However, it needs to be fluid enough to facilitate the flow of writing action.

In the particular case of the present invention, the writing ink may more specifically be a “gel ink” (thus corresponding to a thixotropic ink), especially at 20° C., at rest (shear rate of 0.01 s ⁻¹ ) Viscosities measured at 20° C. at a shear rate of 100 s ⁻¹ using the same rheometer, for example a cone-plate rheometer such as Malvern KINEXUS with a cone of 60 mm and an angle of 1° Unlike, especially higher. In certain embodiments, the viscosity of the gel ink measured under these conditions is between 1,000 and 7,000 mPa.s at a shear rate of 1 s ⁻¹ . s, specifically from 2,000 to 5,000 mPa.s. s, more specifically from 2,500 to 3,500 mPa.s. s, and a shear rate of 5,000 s ⁻¹ , specifically from 5 to 50 mPa.s. s, more particularly from 7 to 40 mPa.s. s, even more particularly between 10 and 20 mPa.s. s range. Specifically, such viscosity is stable during storage for at least 3 months at 40° C. and 20% relative humidity, in particular the viscosity does not have a decrease of more than 50%. More specifically, to avoid static leakage in minutes after writing, the return to viscosity at rest after shearing is very rapid, specifically in a few minutes at most. .

In the sense of the present invention, the term "fixed color" means that the color of the water-based gel ink by visual observation is in particular prior to application onto an absorbent substrate such as paper, cardboard or textile, and onto the absorbent substrate. is intended to mean the same within 7 calendar days (1 week) after application of .

Depending on the content of some ingredients, in particular sodium borohydride ₍ NaBH4), sodium citrate and/or polyvinylpyrrolidone added during the process of preparation of the aqueous ink, the color of the composition can be , changes due to plasmonic effects, and in particular, the color of the composition can change depending on the light absorption by the silver nanoparticles and the space between the silver nanoparticles into the ink composition.

In fact, the plasmonic color is due to light absorption by silver nanoparticles and/or the spacing between silver nanoparticles in the material.

Depending on their size, shape and distance, the color of a dispersion of nanoparticles as well as their properties can change. This is due to plasmon resonance. When silver nanoparticles are exposed to waves of specific frequencies, electrons are concentrated in specific locations, which vary according to the size and shape of the silver nanoparticles. This aggregation of electrons causes anisotropy in the nanoparticles, which in turn leads to changes in light absorption and scattering, resulting in specific colors. Plasmon resonance is also affected by the distance between silver nanoparticles due to their binding. Indeed, the closer the silver nanoparticles are, the more they interact with each other, increasing their binding effect, also called the plasmonic effect. Similarly, shape affects plasmon resonance. In particular, such plasmonic effects can be characterized by UV (ultraviolet)-visible-NIR (near infrared) absorption spectroscopy.

The invention also relates to an aqueous ink with fixed color obtainable by the process of the invention, said aqueous ink comprising silver nanoparticles and polyvinylpyrrolidone.

In the present invention, the gel-based matrix of the water-based ink prepared in step (i) contains 50-95% by weight, specifically 60-90% by weight, more specifically 70-85% by weight of water. obtain.

The aqueous ink gel-based matrix prepared in step (i) may also contain classic gel ink ingredients such as co-solvents, antimicrobial agents, corrosion inhibitors, defoamers, rheology modifiers, and the like. The gel ink raw materials used to prepare the aqueous ink gel-based matrix of step (i) are largely described below in relation to the subject matter of the fixed color aqueous gel inks of the present invention.

Gel-based matrices of water-based inks are prepared by methods well known to those skilled in the art, such as by simple mixing of their ingredients.

In a specific embodiment, the gel-based matrix of the water-based ink does not contain a colorant. Therefore, it does not contain any dyes or pigments. In this case the gel-based matrix of the water-based ink is transparent.

In another specific embodiment, the gel-based matrix of the water-based ink does not contain any reducing agent or any oxidizing agent.

In the present invention, the silver salts are specifically silver such as _AgNO3 , _AgClO4 , _Ag2SO4 , AgCl, AgBr, AgOH, _Ag2O , _AgBF4 , _{AgIO3 , AgPF6} and mixtures thereof ( I) salts, more specifically silver nitrate _AgNO3 . In particular, the silver salt is in the form of an aqueous solution of silver nitrate.

In a specific embodiment, the total amount of silver salt added in step (ii) is 0.0005 to 0.006 wt%, specifically 0.001 to 0.006 wt%, based on the total weight of the aqueous suspension. It is in the range of 0.005% by weight.

Silver nanoparticles are formed when a silver salt is contacted with a reducing agent and an oxidizing agent.

_In the present invention, a mixture of at least an alkali metal or alkaline earth metal salt of citrate, preferably alkali citrate, and an alkali metal hydride, preferably NaBH4, is responsible for the color in step (ii).

In the present invention the alkali metal of the citrate is lithium citrate, sodium citrate, potassium citrate, rubidium citrate, cesium citrate and francium citrate, preferably sodium or potassium citrate, more preferably selected from sodium citrate;

In a specific embodiment of the invention, the alkali metal salt of citrate is sodium citrate.

In the present invention, the alkaline earth metal salts of citrate are beryllium citrate, magnesium citrate, calcium citrate, strontium citrate, barium citrate and radium citrate, preferably magnesium citrate or calcium citrate. , more preferably calcium citrate.

In a specific embodiment of the invention, the alkaline earth metal salt is calcium citrate.

In the present invention, alkali metal hydrides are sodium borohydride (NaBH _{4 )} , sodium cyanoborohydride (NaBH ₃ CN ₎ , sodium triacetoxyborohydride (NaHB(OAc) ₃ ), tri-sec- Sodium butylborohydride, potassium tri-sec-butylborohydride, potassium triethylborohydride, lithium triethylborohydride, lithium tri-sec-butylborohydride, nickel borohydride, lithium aluminate hydride, diisobutyl hydride selected from aluminum, sodium bis(2-methoxyethoxyaluminum hydride);

In a specific embodiment of the invention, the alkali metal hydride is sodium borohydride ₍ NaBH4).

According to a preferred embodiment of the invention, a mixture of sodium citrate and sodium borohydride ₍ NaBH4) is involved in coloring step (ii).

_In particular, the ratio of alkali metal hydride, preferably NaBH4, makes it possible to obtain a specific color in the composition, more particularly in different amounts of alkali metal hydride, preferably _NaBH4 . In particular, this is due to the plasmonic effect exhibited by the composition. For example, the color can change from red to pink to purple to blue with higher amounts of alkali metal hydride, preferably _NaBH4 .

In a specific embodiment, the amount of said citrate added in step (ii) is 0.001 to 0.08 wt%, specifically 0.08 wt%, based on the total weight of the aqueous suspension. 002 to 0.005% by weight.

In a specific embodiment, the amount of alkali metal hydride added in step (ii) is 0.0005 to 0.005 wt%, specifically 0.005 wt%, based on the total weight of the aqueous suspension. 0006 to 0.003% by weight.

The mechanism of colloidal solution formation from the reduction of silver ions consists of two steps: nucleation and growth. The nucleation step requires high activation energy, while the growth step requires low activation energy.

According to a preferred embodiment of the present invention, the process (ii) for preparing an aqueous suspension of silver nanoparticles with a fixed color comprises an additional heating step, e.g. when adding said alkali metal hydride include.

According to a preferred embodiment of the present invention, the process (ii) for preparing an aqueous suspension of silver nanoparticles with a fixed color comprises
- first a silver salt in water and at least an alkali metal or alkaline earth metal salt of citrate, preferably a mixture of alkali citrate and an alkali metal hydride such as _NaBH4 , and an oxidizing agent, preferably peroxide mixing hydrogen H ₂ O ₂ and polyvinylpyrrolidone (step: nucleation);
- an optional heating step;
- mixing the previous composition with a silver salt and an alkali metal hydride, preferably NaBH4 ₍ step: growth).

In a specific embodiment, the molar ratio between the silver salt and the alkali metal or alkaline earth metal salt of at least citrate, preferably a mixture of alkali citrate and alkali metal hydride _NaBH4 , is 0 0.02:1 to 0.10:1, preferably 0.03:1 to 0.06:1.

According to the invention, the oxidizing agent is a C ₁ -C ₈ alkylperoxyacid, such as peracetic acid, acetylcyclohexanesulfonyl peroxide, diisopropylperoxydicarbonate, tert-amyl perneodecanoate, tert-butyl perneodecano. ate, tert-butyl perpivalate, tert-amyl perpivalate, bis(2,4-dichlorobenzoyl) peroxide, diisononanoyl peroxide, didecanoyl peroxide, dioctanoyl peroxide, dilauroyl peroxide, bis(2 -methylbenzoyl) peroxide, disuccinic acid peroxide, diacetyl peroxide, dibenzoyl peroxide, tert-butyl per-2-ethylhexanoate, bis(4-chlorobenzoyl)-peroxide, tert-butyl perisobutyrate, tert-butyl perm Leinate, 1,1-bis(tert-butylperoxy)3,5,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butylperoxyisopropylcarbonate, tert-butylperisononaoate , 2,5-dimethylhexane 2,5-dibenzoate, tert-butyl peracetate, tert-amyl perbenzoate, tert-butyl perbenzoate, 2,2-bis(tert-butylperoxy)butane, 2,2 bis( tert-butylperoxy)propane, dicumylperoxide, 2,5-dimethylhexane-2,5-di-tert-butylperoxide, 3-tert-butylperoxy-3-phenylphthalide, di-tert-amylperoxide, α , α'-bis(tert-butylperoxyisopropyl)benzene, 3,5-bis(t-butylperoxy)3,5-dimethyl 1,2-dioxolane, di-tert-butylperoxide, 2,5-dimethylhexyne -2,5-di-tert-butyl peroxide and 3,3,6,6,9,9-hexamethyl-1,2,4,5-tetraoxacyclononane, hydrogen peroxide H ₂ O ₂ and is selected from a mixture of

Hydrogen peroxide _{( H2O2} ) can be considered a "green" reagent in that its decomposition ultimately leads to the formation of water and oxygen.

According to a preferred embodiment of the invention, the oxidizing agent is hydrogen _{peroxide H2O2} .

In a specific embodiment, the amount of oxidizing agent added in step (ii) is from 0.03 to 0.1 wt%, specifically from 0.04 to It is in the range of 0.08% by weight.

The aqueous suspension of step (ii) also contains polyvinylpyrrolidone. In fact, it stabilizes the silver nanoparticles in suspension and thus avoids any agglomeration.

In a specific embodiment, the amount of polyvinylpyrrolidone added in step (ii) is from 0.05 to 0.1 wt%, specifically from 0.07 to It is in the range of 0.09% by weight.

The aqueous suspension of silver nanoparticles obtained in step (ii) has a fixed color. Its color depends _on the proportion of alkali metal hydride, preferably NaBH4. For example, the color can change from red to pink to purple to blue with higher amounts of alkali metal hydride, preferably _NaBH4 .

In a specific embodiment, the silver nanoparticles obtained in step (ii) have a spherical shape.

Specifically, the silver nanoparticles of the present invention have an average particle size in the range of 1-100 nm, more specifically 10-50 nm. This average particle size is determined by analysis of 2D images (microscope: JEOL ARM 200) according to standard ISO 9001:2015.

In one aspect, the present invention also relates to a process for preparing an aqueous suspension of silver nanoparticles having a fixed color according to step (ii) and to an aqueous suspension obtainable according to step (ii).

The present invention also relates to an aqueous gel ink having a fixed color obtainable by the process of the present invention, said aqueous gel ink comprising silver nanoparticles and polyvinylpyrrolidone, in particular said aqueous ink comprising silver particles stabilized by polyvinylpyrrolidone. Contains nanoparticles.

In particular, compositions according to the invention exhibit a plasmonic effect.

In a specific embodiment, the amount of polyvinylpyrrolidone is 0.05 to 0.1% by weight, specifically 0.1% by weight, based on the total weight of the water-based gel ink with fixed color obtainable by the process of the present invention. 05 to 0.08% by weight.

In the water-based gel ink with fixed color of the present invention, the silver nanoparticles specifically have the shape of spheres.

In the aqueous gel ink with fixed color of the present invention, the silver nanoparticles of the present invention have an average particle size specifically in the range of 1-100 nm, and more specifically 10-50 nm. This average particle size is determined by analysis of 2D images (microscope: JEOL ARM 200) according to standard ISO 9001:2015.

According to a preferred embodiment, the distance between silver nanoparticles in the aqueous gel ink of the present invention is lower than 100 nm, specifically varying from 10-50 nm, more specifically varying from 15-30 nm.

The fixed color of the aqueous gel ink of the present invention is the same as the fixed color of the aqueous suspension of silver nanoparticles obtained in step (ii). Specifically, therefore, silver nanoparticles are the sole colorant of the aqueous gel ink of the present invention. In this case, the water-based gel ink according to the invention does not contain any other colorant than the silver nanoparticles.

In the water-based ink with fixed color of the present invention, more specifically the water-based gel ink, the amount of silver nanoparticles is specifically from 0.0005 to 5% by weight, based on the total weight of the water-based ink, and more Specifically, it is in the range of 0.0007 to 3% by weight.

In the water-based gel ink with fixed color of the present invention, the amount of silver nanoparticles is specifically 0.0005 to 0.005% by weight, more specifically 0.0007, based on the total weight of the water-based gel ink. ~0.002% by weight.

In the aqueous gel ink having a fixed color of the present invention, the amount of water is specifically 50 to 95% by weight, more specifically 60 to 90% by weight, still more specifically 60 to 90% by weight, based on the total weight of the aqueous gel ink. Typically, it ranges from 70 to 85% by weight.

The aqueous inks with fixed color of the present disclosure and the aqueous suspensions obtainable in step (ii) especially comprise alkali metal salts, more particularly sodium salts. In fact, this composition shall be obtained by the process described above using at least an alkali metal hydride and possibly also an alkali metal salt of citrate. When the above process uses an alkaline earth metal salt of citrate, the resulting aqueous ink composition and the aqueous suspension obtainable in step (ii) contain an alkaline earth metal salt in addition to the alkali metal salt. including.

In particular, the amount of alkali metal salts such as sodium salts is at least 0.0003% by weight, in particular 0.0003 ~0.01% by weight.

In particular, when present, the amount of alkaline earth metal is at least 0.00009% by weight, based on the total weight of the aqueous ink and/or based on the total weight of the aqueous suspension, more particularly is in the range of 0.00009% to 0.007% by weight.

The fixed color aqueous gel inks of the present invention may also contain classic gel ink ingredients such as co-solvents, antimicrobial agents, corrosion inhibitors, defoamers, rheology modifiers, etc., as described below. These gel ink components are added to the aqueous ink gel-based matrix in step (i) of the process of the present invention.

The aqueous gel ink of the present invention may contain a co-solvent. Among the co-solvents that can be used are the following - triethylene glycol, polyethylene glycol, diethylene glycol monoethyl ether, diethylene-glycol-monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, phenoxyethanol, phenoxypropanol, etc. glycol ether of
- alcohols: C ₁ -C ₁₅ linear or branched alcohols such as isopropanol, butanol, isobutanol, pentanol, benzyl alcohol, glycerin, diglycerin, polyglycerin;
- esters such as ethyl acetate or propyl acetate,
- carbonate esters such as propylene carbonate or ethylene carbonate,
- water-miscible polar solvents such as methyl isobutyl ketone (MIBK), ketones such as acetone or cyclohexanone, and - mixtures thereof.

In specific embodiments, the co-solvent is selected from the group consisting of glycol ethers, more specifically triethylene glycol, polyethylene glycol, diethylene glycol monoethyl ether, diethylene-glycol-monobutyl ether, dipropylene glycol monobutyl ether. , tripropylene glycol monomethyl ether, phenoxyethanol, phenoxypropanol, and mixtures thereof. In a more specific embodiment, the co-solvent is selected from the group consisting of triethylene glycol, polyethylene glycol, and mixtures thereof.

Specifically, the cosolvent is contained in the aqueous gel ink of the present invention in an amount of 5 to 35% by weight, more specifically 9 to 30% by weight, and even more specifically 11% by weight, based on the total weight of the aqueous gel ink. It is present in amounts ranging from ˜25% by weight.

The aqueous gel inks of the present invention contain isothiazolinones such as ACTICIDE® from Thor, specifically 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and It may contain an antimicrobial agent selected from the group consisting of mixtures thereof.

Specifically, the antibacterial agent is contained in the aqueous gel ink of the present invention in an amount of 0.01 to 0.5% by weight, more specifically 0.1 to 0.2% by weight, based on the total weight of the aqueous gel ink. present in amounts ranging from

Aqueous gel inks of the present invention may specifically include a corrosion inhibitor selected from the group consisting of tolytriazole, benzotriazole, and mixtures thereof.

Specifically, the corrosion inhibitor is contained in the aqueous gel ink of the present invention in an amount of 0.05 to 1% by weight, more specifically 0.07 to 0.5% by weight, based on the total weight of the aqueous gel ink. Even more preferably it is present in an amount ranging from 0.08 to 0.15% by weight.

The aqueous gel ink of the present invention contains an antifoaming agent, specifically a polysiloxane antifoaming agent, more preferably an aqueous emulsion of modified polysiloxane (MOUSSEX® from Synthron, TEGO® Foamex from Evonik). etc.).

Specifically, the antifoaming agent is contained in the aqueous gel ink of the present invention in an amount of 0.05 to 1% by weight, more specifically 0.1 to 0.5% by weight, based on the total weight of the aqueous gel ink. Even more specifically it is present in an amount in the range of 0.2 to 0.4% by weight.

The aqueous gel ink of the present invention is particularly capable of producing a thixotropic phenomenon in which the viscosity is dependent on the time of shear rate and is selected from the group consisting of polysaccharides such as, for example, xanthan gum, gum arabic, and mixtures thereof. may include rheology modifiers capable of producing a gelling effect.

Specifically, the rheology modifier is 0.08 to 2% by weight, more specifically 0.2 to 0.8% by weight, and even more specifically 0% by weight, based on the total weight of the aqueous gel ink. It is present in an amount ranging from 0.3 to 0.6% by weight.

The water-based gel ink having a fixed color of the present invention also
- pH adjusters such as sodium hydroxide and triethanolamine,
-lubricant,
- a coalescing agent,
- a cross-linking agent,
- wetting agents,
- plasticizers,
- antioxidants, and - other additives such as UV stabilizers.

If present, these additives are added to the gel-based matrix of the water-based ink in step (i) of the process of the invention.

SUMMARY OF THE INVENTION In one aspect, the present invention relates to a process for preparing a water-based ink having a fixed color, comprising:
(i) preparing a matrix of aqueous ink;
(ii) a silver salt:
-water,
- an alkali metal or alkaline earth metal salt of at least citrate, preferably a mixture of an alkali citrate and an alkali metal hydride, preferably NaBH4,
- an oxidizing agent, preferably hydrogen peroxide H2O2,
- and polyvinylpyrrolidone, to prepare an aqueous suspension of silver nanoparticles having a fixed color,
(iii) adding the aqueous suspension of silver nanoparticles obtained in step (ii) to the matrix of the aqueous ink obtained in step (i) with stirring to disperse the silver nanoparticles therein; obtaining a water-based ink having a fixed color.

In one aspect, the present invention relates to a water-based ink with a fixed color obtainable by the process of the present invention, wherein the water-based ink comprises silver nanoparticles and polyvinylpyrrolidone, in particular an alkali metal salt as particularly defined in this disclosure. (sodium salts, etc.). It may also contain alkaline earth metal salts.

The fixed color water-based inks of the present invention may also contain classic ink ingredients such as co-solvents, antimicrobial agents, corrosion inhibitors, defoamers, rheology modifiers, etc., as previously described. These raw materials are added to the aqueous ink matrix in step (i) of the process of the present invention.

In one aspect, the invention relates to the use of a fixed color, water-based ink, more particularly a water-based gel ink, as defined above, for writing on an absorbent substrate. In one embodiment, the absorbent support is a porous substrate, specifically paper, cardboard, or textile.

The present invention also relates to a method of writing with a fixed-color, water-based ink, more particularly a water-based gel ink, with a water-based ink having a fixed color according to the invention, on an absorbent material comprising a porous substrate such as paper, cardboard, or textiles. writing on a flexible support.

Silver in water-based inks, more particularly aqueous gel inks, applied onto an absorbent substrate after writing on an absorbent substrate with the fixed color, water-based inks, more particularly aqueous gel inks, of the present invention. The distance between the nanoparticles is lower than 4 μm, specifically varies from 50 nm to 3 μm, more specifically from 500 to 1 μm.

Finally, the present invention relates to a writing instrument, the writing instrument comprising:
- an axial barrel containing an aqueous ink according to the invention, more particularly an aqueous gel ink;
- a pen body that delivers aqueous ink stored in an axial barrel;

The writing instrument of the present invention may be selected from the group consisting of gel pens, felt pens, correction fluids, markers and in particular gel pens.

The invention will be better understood by reference to the examples given in a non-limiting manner.

Example 1: Preparation of water-based gel ink with fixed color according to the process of the present invention A gel-based matrix of water-based ink is prepared (step (i))
In the first step (i), the aqueous ink gel-based matrix was mixed with 15 g triethylene glycol (co-solvent), 4 g polyethylene glycol (co-solvent), 0.19 g Acticide® MBS (antimicrobial agent). , and 0.1 g of Additin® RC8221 (corrosion inhibitor). The mixture is 15 m.p.m.s with a homogenizer mixer. It was homogenized for 15 minutes at a speed of s ⁻¹ and heated to a temperature of 35°C. 0.4 g of xanthan gum (a rheology modifier) was then added to the mixture. The mixture is 15 m.p.m.s with a homogenizer mixer. Homogenized for 15 minutes at a temperature of 35° C. at a speed of s ⁻¹ . 80.01 g of deionized water was slowly added to the mixture. The mixture was allowed to stand for 2 hours and 30 minutes. Then 0.3 g of Moussex® S 9092 (defoamer) was added. The mixture is 15 m.p.m.s with a homogenizer mixer. Homogenized for 30 minutes at a temperature of 35° C. at a speed of s ⁻¹ . The obtained gel-based matrix of water-based ink was cooled at room temperature (25° C.).

Preparing an aqueous suspension of red silver nanoparticles (step (ii))
In a second step (ii), an aqueous suspension of silver nanoparticles with a fixed color was added to 42.527 mL distilled water, 0.473 mL silver nitrate solution (10 mM) (9370.1 Cark Roth), 3.68 mL trisodium citrate (30 mM) (S1804-500G Sigma Aldrich), 3.68 mL polyvinylpyrrolidone 2% (PVP40-100G Sigma Aldrich), and 120 μL hydrogen peroxide 0% (412071 Carlo Erba), 100 μL hydrogenation Prepared by mixing sodium boron NaBH ₄ (100 mM) (71321-25G Fluka Analytical).

The mixture was homogenized with a homogenizer mixer at a speed of 400 rpm for 15-30 minutes.

840 μL of AgNO3 (10 mM) was then added to the mixture with a homogenizer mixer at a speed of 400 rpm for 10 minutes.

The mixture was heated at 100° C., then 350 μL of NaBH ₄ (10 mM) was added.

When _NaBH4 was added to the mixture, the resulting solution instantly changed from clear to colored. This color is due to plasmonic effects.

Stop mixing when the expected red color is obtained.

Note that the color of the aqueous suspension of silver nanoparticles depends _on the ratio of the reducing agent NaBH4. The resulting composition exhibits a plasmonic effect, meaning that its color is due to the plasmonic effect, ie light absorption by the nanoparticle dispersion.

for example:
Addition of 200 μL of NaBH ₄ in the above mixture ensures a pink suspension of silver nanoparticles (test 1).
Addition of 250 μL of NaBH ₄ in the above mixture ensures a bright purple suspension of silver nanoparticles (Test 2).
Addition of 300 μL of NaBH ₄ in the above mixture ensures a purple suspension of silver nanoparticles (test 3).
Addition of 600 μL of NaBH ₄ in the above mixture ensures a blue suspension of silver nanoparticles (test 4).
Addition of 970 μL of NaBH ₄ in the above mixture ensures a red suspension of silver nanoparticles (Test 5).

Preparing an aqueous gel ink with a fixed color (step (iii))
In a third step (iii), 1 mL of the aqueous suspension of silver nanoparticles obtained in step (ii) is added to 1 mL of the aqueous ink gel-based matrix obtained in step (i), A water-based gel ink with a fixed color (red) in which silver nanoparticles are dispersed and stabilized by 0.07% polyvinylpyrrolidone is obtained.

Test 1: After addition of the water-based ink to the gel-based matrix, the initial pink immediately appears pink.
Test 2: After addition of water-based ink to the gel-based matrix, the initial light purple color instantly appears light purple.
Test 3: After addition of water-based ink to the gel-based matrix, the initial purple color appears instantly purple.
Test 4: After addition of water-based ink to the gel-based matrix, the initial blue appears instantly blue.
Test 5: After addition of water-based ink to a gel-based matrix, the initial blue appears instantly red.

Test 1: When the water-based gel ink with fixed color obtained was written on cellulose paper, the color appeared pink instantly and did not change after all.
Test 2: When the water-based gel ink with fixed color obtained was written on cellulose paper, the color appeared bright purple immediately and did not change after all.
Test 3: When the water-based gel ink with fixed color obtained was written on cellulose paper, the color appeared purple instantly and did not change after all.
Test 4: When the water-based gel ink with fixed color obtained was written on cellulose paper, the color appeared blue immediately and did not change after all.
Test 5: When the water-based gel ink with fixed color obtained was written on cellulose paper, the color appeared red instantly and did not change after all. Additionally, a visual assessment of the color of this water-based gel ink was achieved over time (tests 1, 2, 3, 4, 5).

As can be seen from Table 1, the color of the aqueous gel ink did not change over time.

Claims (15)

A process for preparing an aqueous gel ink having a fixed color, comprising:
(i) preparing a gel-based matrix of water-based ink;
(ii) a silver salt:
-water,
- a mixture of at least an alkali metal or alkaline earth metal salt of a citrate, preferably an alkali citrate, more preferably sodium citrate, and an alkali metal hydride, preferably sodium borohydride _NaBH4 ,
- an oxidizing agent, preferably hydrogen peroxide H ₂ O ₂ ,
- and polyvinylpyrrolidone, to prepare an aqueous suspension of silver nanoparticles having a fixed color,
(iii) adding the aqueous suspension of silver nanoparticles obtained in step (ii) to the gel-based matrix of the aqueous ink obtained in step (i) with stirring to obtain silver nanoparticles therein; obtaining an aqueous gel ink having a fixed color in which is dispersed. 2. The process of claim 1, wherein the amount of said citrate added in step (ii) ranges from 0.001 to 0.08% by weight based on the total weight of said aqueous suspension. 3. The process of claim 1 or 2, wherein the total amount of silver salt added in step (ii) ranges from 0.0005 to 0.006% by weight, based on the total weight of said aqueous suspension. Any of claims 1-3, wherein the amount of alkali metal hydride added in step (ii) is in the range of 0.0005-0.005% by weight, based on the total weight of the aqueous suspension. The process of paragraph 1. 5. Any one of claims 1-4, wherein the amount of oxidizing agent added in step (ii) is in the range of 0.03-0.1% by weight, based on the total weight of the aqueous suspension. process described in . 6. Any one of claims 1-5, wherein the amount of polyvinylpyrrolidone added in step (ii) is in the range of 0.05-0.1% by weight, based on the total weight of the aqueous suspension. process described in . The process according to any one of claims 1 to 6, wherein the silver nanoparticles obtained in step (ii) are silver nanoparticles with spherical shape. An aqueous suspension of silver nanoparticles with a fixed color obtainable by the process according to any one of claims 1 to 7, comprising silver nanoparticles and polyvinylpyrrolidone. An aqueous gel ink with a fixed color obtainable by the process according to any one of claims 1 to 7, comprising silver nanoparticles and polyvinylpyrrolidone. It further comprises an alkali metal salt, specifically the amount of the alkali metal salt is at least 0.0003% by weight, especially 0.0003 to 0.01, based on the total weight of the aqueous gel ink or the aqueous suspension. 9. The aqueous gel ink of claim 9 or the aqueous suspension of claim 8 in the weight percent range. An aqueous gel ink according to claim 9 or 10 or an aqueous suspension according to claim 8 or 10, wherein said silver nanoparticles have an average particle size in the range from 1 to 100 nm, in particular from 10 to 50 nm. . The amount of silver nanoparticles is 0.0005 to 5 wt%, specifically 0.0005 to 3 wt%, more specifically 0.0005 to 3 wt%, relative to the total weight of the aqueous gel ink or aqueous suspension. 0005 to 0.005% by weight. The aqueous gel ink according to any one of claims 9 to 12 or claim 8, wherein the amount of water is in the range of 50 to 95% by weight with respect to the total weight of the aqueous gel ink or the aqueous suspension. Or the aqueous suspension according to any one of 10 to 12. - in particular a co-solvent in an amount ranging from 5 to 35% by weight, relative to the total weight of said aqueous gel ink; and/or - in particular, relative to the total weight of said aqueous gel ink 0. antibacterial agents in an amount ranging from 01 to 0.5% by weight, and/or - specifically corrosion inhibitors in an amount ranging from 0.05 to 1% by weight, relative to the total weight of said water-based gel ink; and/or - specifically an antifoaming agent in an amount ranging from 0.05 to 1% by weight relative to the total weight of said aqueous gel ink; and/or - specifically the total weight of said aqueous gel ink. The aqueous gel ink according to any one of claims 9 to 13, further comprising a rheology modifier in an amount ranging from 0.08 to 2% by weight. a writing instrument,
- an axial barrel containing an aqueous gel ink with a fixed color according to any one of claims 9 to 14;
- a pen body delivering an aqueous gel ink according to any one of claims 9 to 14 stored in said axial barrel;
More particularly, said writing instrument is selected from the group consisting of gel pens, felt pens, correction fluids, markers and in particular gel pens.